Door for a shielded enclosure



p 1970 F. E. GARLINGTON 3,531,577

. DOOR FOR A SHIELDED ENCLOSURE Filed July 10, 1968-.

United States Patent 3,531,577 DOOR FOR A SHIELDED ENCLOSURE Frank E. Garlington, Palos Verdes Estates, Calif., as-

signor to Sprague Electric Company, North Adams,

Mass., a corporation of Massachusetts Filed July 10, 1968, Ser. No. 743,850 Int. Cl. Hk 9/00 US. Cl. 174-35 6 Claims ABSTRACT OF THE DISCLOSURE A door closure for an opening in a shielded enclosure comprising a plurality of door panels independently seated against stepped surfaces of a door frame. The panels improve electromagnetic shielding by offering multiple and parallel resistance and reluctance paths to the impinging energy.

BACKGROUND OF THE INVENTION This invention relates to a shielded door enclosure for an opening in a shielded enclosure and, more particularly, to a door assembly having a plurality of independently sealed door panels.

Shielded enclosures serve to protect an enclosed area from external electromagnetic energy or to contain and prevent emanation of electromagnetic energy from within the area. Opeings to these enclosures are unavoidable and fitting a door for these openings presents the problem of maintaining electrical continuity between the door and the frame of the enclosure opening. Stating the problem another way, the resistance and reluctance path across the door frame should be as effective as the like path offered by the walls, ceiling and floor of the enclosure in preventing the entry or exit of electromagnetic energy.

Present door construction techniques utilize one shield panel which is held in place by pressure on a seal gasket or finger stock material placed around the periphery of the door seam. It is impossible, however, to maintain this pressure absolutely equal all along the door seam and, since the resistance and reluctance pressure at any given point along the seam will vary according to the pressure at that point, some electromagnetic and electrostatic leakage inevitably ensues, particularly the for-mer. Since there is only one panel, such leakage constitutes an immediate contamination of the enclosure or dissipation of the energy source within the enclosure. This leakage problem is further complicated in the so-called double isolated rooms which require inner and outer shielding layers.

A still further problem encountered in manufacturing the single door frame is the tight tolerances required for the formed sheet metal work.

SUMMARY OF THE INVENTION Broadly, the present invention is a shielded door closure assembly for shielded enclosures which is set into a door frame with recessed mounting surfaces designed to seat the assembly. More specifically, the assembly comprises a plurality of shielded door members; each member is independently seated in the frame in parallel rela tion to each other and to the enclosure wall in which the frame is mounted. Means are provided for adjusting the degree of adhesion of each door member to the surface of the frame on which it is seated.

In the preferred embodiment, two shielded metal panels are connected together to form the door assembly. Each panel has mesh gasket, finger stock means or the like around the perimeter of the surface facing the interior of the enclosure. The panels are seated against separate surfaces of the door frame, contact being made at the gasket area. Biasing means are provided for uniformly pressing the panels against the frame along selected portions of the panel perimeter. These means are independently adjustable to allow for variation in the panel to frame adhesion.

When each door member is fully seated in the closed position, positive electrical contact is made between the member and the door frame through the gasket means. The direct contact seal thus provided alfords both good conductivity and high permeability. Each seated member provides parallel resistance and reluctance paths for the energy to be shielded; hence any energy leakage which occurs through the outer door member because of insulficient or unequal biasing pressure will be attenuated by the succeeding inner members. This obviates the problem of energy leakage through the single member closure which would directly contaminate the enclosures interior. This configuration, in comparison to prior art, provides significant improvement in electromagnetic shielding and at least equivalent shielding of electric field and plane waves.

Because of this back-up feature, the close tolerances on door manufacture required to insure maximum electrical contact to the frame can be relaxed reducing the cost of jigs, fixtures, special machine work and skilled labor and thereby reducing construction costs. Further, the materials used in the present invention are standard mill forms, eliminating the need for special order items.

The invention also provides an improved means for shielding double isolated rooms; the door frame can be designed to extend from the outer to the inner wall with each panel being insulated from each other and seated so as to form part of the wall.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a general elevational view of a shielded door assembly in place in a shielded enclosure;

'FIG. 2 is a cross-setional view of FIG. 1 taken along line 22;

FIG. 3 shows the invention using more than 2 panels in a door assembly;

FIG. 4 is a partial view of an alternate embodiment of the invention showing door panels opening in opposite directions; and

FIG. 5 is a partial view of the invention used with a double-shielded type of enclosure.

DESCRIPTION OF THE INVENTION In the drawings, FIG. 1 shows the preferred embodiment of the shielded door assembly 2 in a wall 3 of a shielded enclosure. FIG. 2 is a cross-sectional view through line 2-2 of FIG. 1 showing panels 4 and 5 connected together by a plurality of right angle steel brackets 6 to form the door assembly. A plurality of compression springs 7 are mounted between panels 4 and 5 around core members 8. Gasket elements 9 and 10 are A thick by 1" wide strips of a woven ferromagnetic mesh which are secured to, and extend around, the perimeter of the inward-facing surface of panel 4; gasket element 11 is a mesh strip of similar dimensions and properties which extends around the inward-facing surface perimeter of panel 5. Handle 12 is provided to swing the door assembly open or closed about hinges 13. The door hinges are ball-bearing, double axis articulated devices which allow all closing pressure to be applied perpendicular to the door.

Referring to FIGS. 1 and 2, the aperture into which door assembly 2 is seated is irregularly shaped and is defined by two surfaces of door frame 14. The edge of outer surface 15 of the frame defines the widest point of the aperture while the edge of recessed surface 16 defines the narrowest point.

Panel 4 is a steel plate physically wider than plate 5 since it covers the wider aperture dimension. The panel 4 contacts surface 15 by means of gasket strips 9 and 10 thereby establishing an electrical connection between opposing surfaces across panel -4 and along the entire perimetric extent of the panel. The quality of this connection; that is, its resistance and reluctance characteristics, vary with the pressure applied against panel 4, strips 9 and 10 and surface 15. This pressure is derived from hydraulically actuated swing clamps (not shown) and is perpendicularly applied to a plurality of pads 17 which are strategically located along the outside perimeter of panel 4 so as to facilitate application of as uniform a pressure as possible to strips 9 and 10*.

Panel 4 is structurally connected to panel 5 to form an assembly by means of physically identical right angle brackets *6. These brackets are connected by guide pins 6A having some degree of travel within slots 6B. The brackets may extend across the entire width and/or length of the panels 4 and 5 or may be individually located along selected points. However connected, they must provide support between the two panels maintaining them in proper relationship. Panel 5 is also a steel plate, physically smaller than panel '4, since it covers the narrower aperture dimension. The panel 5 contacts surface 16 by means of gasket strip 11 thereby establishing an electrical connection between the opposing surfaces 16 across panel 5 and along the entire perimetric extent of the panel. As with panel 4, the quality of this connection is dependent upon the pressure applied at the contact points. This pressure is applied and maintained by mounting a plurality of compression springs 7 between panels 4 and 5 and along the outside perimeter of the latter, so as to perpendicularly apply pressure to gasket strip 11. The springs are detachably mounted around guide elements 8 which are, in turn, fixedly mounted in panel 4. The required pressure is predetermined and the springs are selected to provide the required pressure when confined to the set space between the panels. Guide pins 6A cooperate with the springs by permitting some play between panels. While compression springs are preferred, any means of force transmission might be used in place of the springs such as hydraulic or pneumatic pistons or bellows or leaf springs.

The advantages of the invention now become more obvious. Panels 4 and 5 have been independently seated into frame 14 and form parallel electrical paths across separate surfaces 15 and 16 of the frame. The degree of adherence to the respective surface to which they are mounted are independently set and adjusted. While it is still desirable that the resistance and reluctance of these paths be as uniform as possible with that of the enclosure wall, the affordable tolerance at the door clearance perimeter has been eased. Thus, even should the pressure on outer panel 4 be non-uniform to some extent resulting in leakage along surfaces 15, the shielding along the second path across panel 5 will effectively block this stray leakage. This is in contrast with a single panel closure wherein any leakage across the door clearance perimeter results in immediate contamination. Along with a relaxation of pressure tolerance, there is no requirement, as with a single panel door, for flanges and the like connected to the door. These flanges must be constructed with tight tolerance to match the adjacent plane of the enclosure aperture.

The above described embodiment provides effective electromagnetic shielding over a range of 1 Hz. to 34 gHz. with a pressure of approximately 25 psi. applied to gaskets 9, 10 and 11.

Under more intense energy bombardment, it may be necessary to add additional panels to provide still further attenuation. An alternate embodiment, shown in partial end view in FIG. 3 shows, in addition to panels 20 and 21, additional panel 22 set against additional recessed surfaces 23 of the door frame. The panel is structurally connected, as previously described, to right angle frame 24 and is biased against surface 23 via gasket strip 25. The door assembly then consists of three panels, each panel providing a separate parallel path across the enclosure aperture. As many additional panels could be thus provided as necessary.

Additional modifications could be added without departing from the spirit and scope of the invention. For example, panels 26 and 29' could be physically separated as shown in FIG. 4, each With its own closure pressure means placed against gasket strips 27, 28 and ,31 respectively. The panels could also be opened and closed by separate hinging means; the outer panel 26 could be swung outward while inner panel 29, mounted on surface 30, could be swung inward.

This flexibility is illustrated in FIG. 5 wherein is assembled a door closure for a doubled isolated enclosure. In this type of enclosure inner shielding wall and outer shielding wall 34 must be physically and electrically isolated from each other as by dielectric material 36. In this instance panel 37 would be mounted on the outside surface of wall 34 as previously described while panel 38 is mounted on the inner surface of wall 35. Thus there is still a second electrical contact path present to intercept energy leaking through the first panel closure area. To preserve the isolation between walls 34 and 35, bracket 39 and spring 40 which otherwise function as previously described, should be insulated.

Although the panel embodiment of FIG. 1 shows the outer panel protruding from the enclosure wall surface, the frame could be indented at the panel contact point so that the panel would lie flush with the enclosure wall, or even indented in relation to the wall.

While the panels in the preferred embodiment were steel, both panels could be another ferrous material; both could be copper or any good conductor or, alternatively, the panels could be a combination of former and latter materials.

Also, the gasket strips, instead of being fixed to the door, might be placed on the edges of the frame surfaces in the area where the panels are to be seated. Performance is the same :with the gasket in either position.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention it is to be understood that the invention is not limited to said details.

What is claimed is:

1. An electromagnetic shielded closure for a shielded enclosure comprising:

a door frame forming part of a wall of said enclosure and providing a plurality of stepped, recessed perimetric surfaces;

a plurality of magnetically shielded door members flexibily connected in substantial parallel relation to each other, the space between said door members and the dimensions of each door member designed so that each door member is seated against one of said surfaces;

at least one elongated strip of resilient electric conductive material positioned between the complete perimeter of each door member and the perimeter of the frame surface against which it is seated;

means for separately biasing each door member against said strip conductive material and the frame surface against which said door member is seated; said biasing means being applied along the length of said strip conductive material and perpendicular to it; and

means for opening and closing each door member.

2. A shielded closure as described in claim 1 wherein said door members form a door assembly and including hinged means for opening and closing said door assembly.

3. A shielded clousre as described in claim 2 wherein the means for biasing those door members other than the outer door member comprises a plurality of compression springs positioned in the spacing between said parallel members and perpendicular to the elongated conductive strip and frame surface area against which the bias is applied.

4. A shielded closure as described in claim 1 where said resilient electric conductive material is woven ferromagnetic mesh.

5. A shielded closure as described in claim 1 wherein said perimetric surfaces extend inwardly into the enclosure so as to define a progressively narrower aperture and wherein said door members are of progressively smaller dimensions, the outer door member being the largest and each member being seated against an outward-facing perimetric surface.

6. An electromagnetic shielded closure for a double isolated wall shielded enclosure comprising:

two magnetically shielded electrically isolated door members flexibly connected in substantial parallel relation to each other seated against the frame of each of said isolated walls; the space between the door members and the dimensions of each door member designed so that each door member is seated against an outward-facing perimetric surface of said walls;

at least one elongated strip of resilient electric conductive material positioned between the complete outer edge of each of said door members and the isolated wall surface against which it is seated;

means for separately biasing each door member against the perimetric surface against which it is seated; and

means for opening and closing each door member.

References Cited UNITED STATES PATENTS 2,757,225 7/1956 Dunn. 2,853,541 9/1958 Lindgren. 3,055,969 9/1962 Schaller. 3,236,935 2/1966 Patton.

DARRELL L. CLAY, Primary Examiner US. Cl. X.R 

